Mirroring edge pixels

ABSTRACT

Techniques are described that enable a two-dimensional (2D) representation of three-dimensional (3D) virtual reality content to be generated and encoded. These techniques include modifying non-display pixels within the 2D representation to soften the transitions between display pixels and non-display pixels.

BACKGROUND

Virtual reality (VR) is a computer technology that replicates an environment, real or imagined, and simulates a user's physical presence in the environment and, in some cases, enables the user to interact with the environment. Typically, virtual reality content is displayed on a computer monitor or with a virtual reality device such as a virtual reality headset, which is also commonly referred to as a head-mounted display. The user may interact with the environment by interacting with the virtual reality device, through the use of a standard input device such as a keyboard or mouse, or through a multimodal device such as a wired glove. As the user interacts with the environment, three-dimensional (3D) images are provided by virtual reality software that accesses virtual reality content.

The original source images from which VR content is constructed correspond to different perspectives from the user's location within the virtual environment. In the typical work flow by which VR content is generated, these images are combined in a process known as “stitching” to form a two-dimensional (2D) representation (using, for example, polygonal or equirectangular projection) in which each of the images corresponds to a portion of a three-dimensional (3D) shape such as, for example, a cube or a cylinder. The 2D representation is then compressed using any of a variety of encoding techniques such as, for example, H.265/High Efficiency Video Coding (HEVC) or H.264/MPEG-4 Advanced Video Coding (H.264).

A 2D representation generated by a stitcher can include non-display pixels that do not contain image content. As a result, the 2D representation that is encoded can include sharp edges that separate the stitched VR content from regions of non-display pixels. During playback of the VR content, visual artifacts can result, detracting from the user's experience.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an example of a 2D representation generated from 3D content that has been modeled using a polygonal projection space.

FIG. 1B illustrates another example of a 2D representation generated from 3D content that has been modeled using a polygonal projection space.

FIG. 2 illustrates an example of a particular implementation.

FIG. 3 is a simplified diagram of a computing environment in which various implementations may be practiced.

FIG. 4 is a simplified diagram of an example of a client device with which various implementations may be practiced.

FIG. 5 is a flowchart illustrating a method of modifying edge pixels according to various implementations.

DETAILED DESCRIPTION

This disclosure describes techniques that modify non-display pixels that are immediately adjacent to display pixels within a two-dimensional (2D) representation of virtual reality (VR) content. By modifying non-display pixels, edges separating non-display pixels from display pixels are softened.

In accordance with various implementations, non-display pixels within a 2D representation of VR content are modified based, at least in part, upon display pixels within the 2D representation. More particularly, pixel values of non-display pixels that are adjacent to display pixels within the 2D representation are modified based upon pixel values of the adjacent display pixels. Where the VR content is represented by grayscale images, each pixel can be represented by a single pixel value that represents the brightness (i.e., intensity) of the pixel. In some implementations, non-display pixels are modified to replicate display pixels. In other implementations, the non-display pixels are modified to include an average pixel value of adjacent display pixels. Modification of display pixels may be performed along a vertical and/or horizontal axis.

Telecommunications networks and other content services commonly stream video to client devices for display on televisions and computer monitors. With the increase in availability of three-dimensional (3D) virtual reality content, some content services offer the streaming of 3D virtual reality content. The virtual reality content offers a user the ability to view their virtual environment from a number of viewer-selected perspectives.

To generate a 3D virtual reality environment, a virtual cube, cylinder, or other three-dimensional shape is typically used to display images of the virtual reality environment as they would be perceived by a user within the virtual reality environment. For a given user position or perspective within the virtual reality environment, there will often be 6 (or more) possible images corresponding to the faces of the three-dimensional shape. More particularly, an image may be generated and displayed for each of the faces of a virtual cube, cylinder, or other three-dimensional shape (or projection space) that would be visible from the perspective of the user within the virtual reality environment at a given point in time.

A number of polygonal projection spaces can be used to represent 3D virtual content. For example, the 3D content may be represented using a hexahedron (having 6 faces), a cube (having six faces), an octahedron (having 8 faces), a dodecahedron (having 12 faces), or an icosahedron (having 20 faces).

When images of virtual reality (VR) content corresponding to the different faces of a virtual three dimensional 3D polygonal projection space are mapped to a 2D representation such as a rectangular representation, the resulting 2D representation can include a number of non-display pixels in regions of the 2D representation that do not include 3D content. A non-display pixel is a pixel that does not contain source image content, while a display pixel is a pixel that contains source image content. For example, a non-display pixel may be represented by a set of pixel values that are each zero.

FIG. 1A illustrates an example of a 2D representation generated from 3D content that has been modeled using a polygonal projection space. In this example, 3D content modeled using a cube is mapped to a 2D representation 102. Images corresponding to the 6 faces of the cube are represented by blocks 104, 106, 108, 110, 112, and 114. Regions 120 and 122 within 2D representation 102 represent non-display pixels. In this example, each of the edges separating regions 120, 122 containing non-display pixels from regions 104, 106, 108, 110, 112, 114 containing display pixels is parallel to either a horizontal or vertical axis.

FIG. 1B illustrates another example of a 2D representation generated from 3D content that has been modeled using a polygonal projection space. In this example, representation 140 is a 2D representation of 3D content modeled using an icosahedron. Display pixels corresponding to stitched VR content are represented by region 142, while non-display pixels form remaining triangular regions 144-166 of representation 140. As shown in FIG. 1B, triangular regions 144-166 are immediately adjacent to portions of stitched VR content represented by region 142. Edges separating region 142 containing display pixels from triangular regions 144-166 containing non-display pixels are diagonal.

When a 2D representation is generated from 3D content, the 2D representation will typically include regions that contain non-display pixels. As a result, the 2D representation will typically include sharp lines at edges (e.g., borders) of stitched VR content that are immediately adjacent to non-display pixels. As shown in representations 130 and 140, region(s) containing display pixels are each separated from region(s) containing non-display pixels by a sharp edge.

The minimum block size that can be used to encode the VR content is often insufficient to separate high intensity regions from low intensity regions. Separation of high intensity regions from low intensity regions is particularly difficult when a 2D representation includes diagonal lines, as shown at 140. When a block of the VR content is encoded, the high spatial frequencies that correspond to the transition between low intensity (e.g., black) non-display pixels and adjacent high intensity (e.g., white) display pixels cannot be accurately captured. As a result, visual artifacts are likely to result along borders of the stitched VR content that abut regions of non-display pixels within the 2D representation.

During playback of virtual reality content, the 2D representation is typically scaled to a playback projection space. Pixels that do not contain visible content are typically ignored. When the edges along the borders of the stitched VR content within the 2D representation are matched up within the playback projection space, visual artifacts resulting from the encoding of the transitions between display and non-display pixels can detract from the user's experience.

FIG. 2 illustrates the operation of an example of a particular implementation. 3D virtual reality content 200 including one or more images may be received or retrieved. The images all correspond to the same instant of time and correspond to the different faces of a 3D shape (or polygonal projection space).

3D virtual reality content 200 is mapped to a 2D representation 202. This is typically accomplished by a “stitcher” that stitches the images together in a 2D plane to generate the 2D representation 202. Edge pixel modification 204 is performed to soften edges between display and non-display pixels, as will be described in further detail below.

In accordance with various implementations, encoding 206 is performed after edge pixel modification 204 has been performed. Edge pixel modification can be performed by a module such as a stitcher that generates the 2D representation of the content. Alternatively, edge pixel modification may be performed by an encoder prior to or in conjunction with encoding.

3D content corresponding to further time instants may be processed in a similar fashion. File(s) 208 storing encoded frame(s) for the 3D content 200 for corresponding time instant(s) may be stored in association with various virtual reality titles.

A user of client device 210 browses a catalogue of virtual reality titles available from service 212. When the user selects one of the titles, content service 212 streams content corresponding to the selected title to client device 210. The streaming of content to client device 210 is facilitated by software installed on client device 210. For example, the software may include virtual reality software that facilitates the rendering of virtual reality content. The software operates to provide 3D content via a display that is integrated with client device 210 (as shown) or coupled to client device 210.

Service 212 maintains files 208 associated with the titles available from service 212 that enable virtual reality content to be streamed to client devices using service 212. In this example, service 212 selects file(s) 208 that are relevant to the selected title. File 208 is a video file that includes frames 214 that have been encoded by a video encoder that operates according to a video encoding standard such as H.264 or H.265. In another implementation, virtual reality content may be generated and encoded dynamically using these or other codecs.

In one implementation, content service 212 provides information pertaining to the fragments of the virtual reality content to client device 210. For example, content service 112 may provide a manifest file that indicates locations (e.g., URLs and/or byte offsets) at which the fragments or portions thereof can be accessed. Client device 210 can use the manifest to download fragments or portions thereof. For example, client device 210 can download a fragment header including a fragment index that can be used to download frames.

Logic 214 of client device 210 may download video fragment(s) from content service 212 and store the fragment(s) in memory 216 (or buffer). Alternatively, logic 214 may selectively download individual frames that correspond to different faces of the 3D projection space from content service 212 and store the frames in memory 216.

As logic 214 selects frames for decoding, logic 214 provides the selected frames to a video decoder 218. Video decoder 218 decodes the frames to generate the corresponding digital images representing the various views of the virtual reality environment. Images that are rendered produce fewer visual artifacts than conventional systems that do not implement pixel edge modification. Therefore, the virtual reality experience of a user can be improved significantly.

FIG. 3 illustrates an example of a computing environment in which a service 302 such as a content service provides virtual content via network 304 to a variety of client devices (306-1 through 306-5) in accordance with the techniques described herein. More particularly, the content may include virtual reality video-on-demand (VOD) content or broadcast content (e.g., 3D video of live events).

Content service 302 includes content delivery logic 310 which facilitates various aspects of content delivery to client devices 306. Content service 302 may conform to any of a wide variety of architectures such as, for example, a services platform deployed at one or more co-locations, each implemented with one or more servers 303. Network 304 represents any subset or combination of a wide variety of network environments including, for example, TCP/IP-based networks, telecommunications networks, wireless networks, satellite networks, cable networks, public networks, private networks, wide area networks, local area networks, the Internet, the World Wide Web, intranets, extranets, etc. Client devices 306 may be any suitable device capable of connecting to network 304 and downloading or consuming streams of VOD or broadcast content provided by service 302. Such devices may include, for example, mobile devices (e.g., cell phones, smart phones, and tablets), personal computers (e.g., laptops and desktops), set top boxes (e.g., for cable and satellite systems), smart televisions, gaming consoles, wearable computing devices (e.g., smart watches, smart glasses, or virtual reality headsets), etc.

At least some of the examples described herein contemplate implementations based on computing models that enable on-demand network access to a shared pool of computing resources (e.g., networks, servers, storage, applications, and services). As will be understood, such computing resources may be integrated with and/or under the control of the same entity controlling content service 302. Alternatively, such resources may be independent of content service 302, e.g., on a platform under control of a separate provider of computing resources with which content service 302 connects to consume computing resources as needed.

It should also be noted that, despite any references to particular computing paradigms and software tools herein, the computer program instructions on which various implementations are based may correspond to any of a wide variety of programming languages, software tools and data formats, may be stored in any type of non-transitory computer-readable storage media or memory device(s), and may be executed according to a variety of computing models including, for example, a client/server model, a peer-to-peer model, on a stand-alone computing device, or according to a distributed computing model in which various functionalities may be effected or employed at different locations.

In the following examples and for the sake of simplicity, content service 302 is described as if it were integrated with the platform(s) that provides the content to client devices. However, it will be understood that content service 302 may provide access to content in conjunction with one or more content delivery networks (e.g., CDN 304) that may or may not be independent of content service 302. In addition, the source of the content may or may not be independent of content service 302 (e.g., as represented by content provider server 316).

Implementations enabled by the present disclosure contemplate logic and video decoder(s) resident on the client devices consuming content from content service 302; such logic and video decoder(s) being configured to download and decode frames of 3D video files as described herein and display the resulting images. The logic and/or decoder(s) might be part of an existing algorithm or module on the client device or implemented to work in conjunction with such an algorithm or module. The logic and/or decoder(s) might be implemented, for example, in a media player on the client device, as a browser plug-in, or as a separate application or module resident on the client device.

Implementations are also contemplated in which, in addition to content delivery logic 310 (which facilitates various aspects of content delivery to client devices 306), content service 302 includes logic that facilitates at least some aspects of the encoding of content as described herein (e.g., as represented by content encoding logic 311 and stitching logic 313). In some implementations, stitching logic 313 or other pixel modification logic can perform edge pixel modification. In other implementations, encoding logic 311 might perform edge pixel modification. In addition, encoding logic 311 may encode frames according to a specified or variable block size to reduce or minimize the number of non-display pixels in blocks that contain source image data (e.g., display pixels).

The frames associated with 3D virtual reality content may be encoded according to a particular video encoding standard or multiple encoding standards. More particularly, encoding logic 311 can employ one or more video encoders 314, where each video encoder 314 operates according to a different video encoding standard. As will be appreciated, video encoding can be implemented in software and/or hardware.

In some implementations, content service 302 also includes stitching logic 313. Stitching logic 313 may generate a 2D representation from 3D virtual content corresponding to a particular instant of time. For example, stitching logic 313 may stitch images corresponding to the faces of a 3D shape (or projection space) such that a 2D representation is generated. The 2D representation may include a grid of pixels or pixel values. Edge pixel modification may be performed by stitching logic 313 and/or encoding logic 311. In some instances, stitching logic 313 may provide metadata to encoding logic 311 to enable encoding logic 313 to perform edge pixel modification or facilitate encoding. For example, the metadata may identify edges within the 2D representation, indicate which display pixels are to be used to modify non-display pixels, and/or indicate non-display pixels that are to be modified.

In addition to providing access to content, content service 302 may also include a variety of information related to the content (e.g., manifests or other metadata) in data store 312 to which service 302 provides access. Alternatively, such information about the content, as well as the content itself may be provided and/or hosted by one or more separate platforms, e.g., CDN 304. It should be noted that, while logic 310, 311, and 313, video encoder 314, and data store 312 are shown as integrated with content service 302, implementations are contemplated in which some or all of these operate remotely from the associated content service, and/or are under the control of an independent entity. From these examples, those of skill in the art will understand the diversity of use cases to which the techniques described herein are applicable.

A block diagram of an example of a client device 400 suitable for use with various implementations is shown in FIG. 4. Device 400 includes one or more single or multi-core processors 402 configured to execute stored instructions (e.g., in device memory 424). Device 400 may also include one or more input/output (I/O) interface(s) 404 to allow the device to communicate with other devices. I/O interfaces 404 may include, for example, an inter-integrated circuit (I2C) interface, a serial peripheral interface (SPI) bus, a universal serial bus (USB), an RS-242 interface, a media device interface, and so forth. I/O interface(s) 404 is coupled to one or more I/O devices 406. The I/O device(s) 406 may include one or more displays 406(1), one or more haptic generators 406(2), a touch sensor array 406(3), one or more accelerometers 406(4), one or more image capture systems 406(5), one or more motion sensors 406(6), one or more orientation sensors 406(7), microphones, speakers, and so forth.

User interaction with a virtual reality environment may be detected via one or more of the I/O devices 406. For example, a position or perspective of a user in relation to his or her virtual reality environment may be detected via one or more of the I/O devices 406. Based upon the current position or perspective (e.g., angle) of the user within the virtual reality environment, device 400 may decode or display portions of the virtual reality environment that are visible from the user's current position/perspective.

Device 400 may also include one or more communication interfaces 408 configured to provide communications between the device and other devices. Such communication interface(s) 408 may be used to connect to cellular networks, personal area networks (PANs), local area networks (LANs), wide area networks (WANs), and so forth. For example, communications interfaces 408 may include radio frequency modules for a 3G or 4G cellular network, a WiFi LAN and a Bluetooth PAN. Device 400 also includes one or more buses or other internal communications hardware or software (not shown) that allow for the transfer of data and instructions between the various modules and components of the device.

Device 400 also includes one or more memories (e.g., memory 410). Memory 410 includes non-transitory computer-readable storage media that may be any of a wide variety of types of volatile and non-volatile storage media including, for example, electronic storage media, magnetic storage media, optical storage media, quantum storage media, mechanical storage media, and so forth. Memory 410 provides storage for computer readable instructions, data structures, program modules and other data for the operation of device 400. As used herein, the term “module” when used in connection with software or firmware functionality may refer to code or computer program instructions that are integrated to varying degrees with the code or computer program instructions of other such “modules.” The distinct nature of the different modules described and depicted herein is used for explanatory purposes and should not be used to limit the scope of this disclosure.

Memory 410 includes at least one operating system (OS) module 412 configured to manage hardware resources such as I/O interfaces 404 and provide various services to applications or modules executing on processor(s) 402. Memory 410 also includes a user interface module 416, content decoding module 420, content rendering module 422, and other modules.

Content decoding module 420 may select frames to decode and sends the selected frames to a video decoder 248. In some implementations, a demultiplexer (DEMUX) 426 may demultiplex frames of fragments and pass the demultiplexed frames to decoder 428 for decoding.

Video decoder 428 includes software and/or hardware (e.g., electrical components or a circuit) configured to decode frames of video content files according to a corresponding video encoding standard such as H.265. In accordance with various implementations, decoder 428 is agnostic to edge pixel modification that has been performed. In other implementations, decoder 428 decodes frames based, at least in part, on metadata pertaining to edge pixel modification.

Content rendering module 422 may render virtual reality content based on the decoded frames. Generally, content is rendered according to the user's position/perspective within the virtual reality environment and the timestamps of the frames.

Memory 410 also includes device memory 424 to store a wide variety of instructions and information using any of a variety of formats including, for example, flat files, databases, linked lists, trees, or other data structures. Such information includes content for rendering on display 406(1) including, for example, any type of video content (e.g., frames, fragments, or video files). In some implementations, a portion of device memory 424 may be distributed across one or more other devices including servers, network attached storage devices, and so forth.

The logic or computer program instructions used to support the downloading, decoding, and rendering of virtual reality content may be implemented in a variety of ways. For example, at least some of this functionality may be implemented as part of the code of a media player operating on device 400. Alternatively, at least some of this functionality may be implemented separately from and interact with the device's media player, web browser, mobile app, decoder, etc. The range of possibilities will be understood by those of skill in the art with reference to the following description.

It will also be understood that device 400 of FIG. 4 is merely an example of a device with which various implementations enabled by the present disclosure may be practiced, and that a wide variety of other device types including, for example, virtual reality headsets may also be used. The scope of this disclosure should therefore not be limited by reference to device-specific details.

In accordance with various implementations, a 2D representation generated from source images is modified prior to encoding the 2D representation. Modification of the 2D representation is performed by modifying non-display edge pixels, thereby reducing visual artifacts and improving the efficiency of the encoding process,

FIG. 5 is a flowchart illustrating a method of modifying edge pixels according to various implementations. Images of virtual reality (VR) content corresponding to portions (e.g., faces) of a virtual three dimensional (3D) projection space are mapped to a two dimensional (2D) representation (502). For example, the 3D projection space may include a polygonal projection space that corresponds to a hexahedron, a cube, an octahedron, a dodecahedron, or an icosahedron. The 2D representation may be a rectangular representation represented by a 2D array, where each element of the array corresponds to a different pixel

After the 2D representation has been generated or otherwise obtained, edge pixel modification may be performed for each edge within the 2D representation. The process of performing edge pixel modification for a single edge is described below with reference to steps 504-512.

An edge within the 2D representation is identified (504), where the edge separates a first region containing non-display pixels from a second region containing display pixels of the VR content. The second region corresponds to a view or face of the 3D projection space, while the first region includes non-display pixels that are immediately adjacent to the second region. The edge may be identified by performing edge detection on a per-pixel basis. More particularly, edge detection may include the analysis of pixel values to ascertain points at which image brightness changes sharply. Alternatively, the edge may be identified through the use of a map of pixels that identifies edges within the 2D representation. For example, the map may identify display pixels adjacent to an edge, an image containing the display pixels adjacent to the edge, block(s) containing the display pixels adjacent to the edge, and/or non-display pixels that are adjacent to the display pixels.

At least a portion of the second region is identified for use in pixel modification (506). The portion of the second region can be identified, for example, using a map of pixels or based upon pixel analysis. The portion of the second region can include pixels immediately adjacent to the edge and/or pixels in close proximity to the edge. In some implementations, the portion of the second region includes only a subset of the display pixels within the second region. For example, the portion of the second region can consist of a block of pixels defined by an encoder.

A pixel value for each of the display pixels of the portion of the second region is identified (508). For example, a pixel value may include an intensity value. As another example, a pixel value may include color information. Color information may represent a component of a color of the pixel, such as a red component, a green component, or a blue component.

For each of the non-display pixels of the first region, a corresponding replacement pixel value is determined based, at least in part, on the pixel value of at least one of the display pixels of the portion of the second region (510). In some implementations, all of the display pixels in the second region are used for edge pixel modification. In other implementations, the display pixels of only a portion of the second region are used for edge pixel modification. For example, edge pixel modification may be performed based upon display pixels within a particular block of pixels within the second region.

Each of the non-display pixels of the first region may be modified to include the corresponding replacement pixel value (512). In some instances, the replacement pixel value will be the same for all of the non-display pixels within the first region. For example, the replacement pixel value may be the average pixel value of the display pixels within the second region or portion thereof (e.g., block of pixels). As another example, the replacement pixel value may be 0 or 1. In other instances, the replacement pixel value of a non-display pixel may replicate the pixel value of a specific display pixel. For example, the replacement pixel value for each of the non-display pixels within the first region may mirror, along a horizontal and/or vertical axis, the pixel value of a corresponding display pixel of the second region. It may be desirable, for example, to mirror pixel values of a block of display pixels. In other instances, replacement pixel values for the non-display pixels of the first region may be interpolated from the values of the display pixels within the second region. In yet other instances, replacement pixel values for the non-display pixels of the first region may be extrapolated from pixel values of the display pixels within the second region. Replacement pixel values may be extrapolated through prediction by a filter such as a sinc function.

Steps 504-512 may be repeated for each edge within the 2D representation. Edge pixel modification results in the softening of edges within the 2D representation, thereby improving coherency at the edges of the VR content. Therefore, the potential for visual artifacts at edges of the VR content is significantly reduced.

After edge pixel modification has been performed for all edges within the 2D representation, pixels corresponding to the 2D representation may be encoded. An encoder may exploit redundancies within the VR content resulting from edge pixel modification. More particularly, where the same pixel value is used for a region of non-display pixels, the encoder may more efficiently encode the pixels due to the redundancy of pixel values. Similarly, where a block of display pixel values is mirrored in a region of non-display pixels, the encoder may use the replication of the block of pixel values to more efficiently encode the 3D virtual content. Therefore, by modifying non-display pixels adjacent to the edges of the VR content, the number of bits required to encode the VR content may be reduced.

In some implementations, an encoder may encode pixels according to a variable block size to minimize the number of non-display pixels that are encoded in blocks that contain image data (e.g., display pixels). For example, an encoder may select an optimal block size and/or shape to encode a particular edge section. In other implementations, a smallest block size supported by a particular encoder may be used to ensure that the number of non-display pixels that are encoded is minimized.

Edge pixel modification may be performed by a stitcher, an encoder, or another intermediate process. After edge pixel modification has been performed, a stitcher or other module may instruct an encoder to encode pixels including the display pixels and non-display pixels. For example, an array of pixel values or pointer thereto may be provided to the encoder. The encoder may be instructed to encode the pixels according to a variable block size or a specified block size. In addition, metadata pertaining to edge pixel modification may be provided to the encoder to facilitate the encoding process. The metadata may indicate, for example, regions containing display pixels, regions containing non-display pixels, regions containing modified pixels, etc.

In some implementations, a decoder is agnostic to the edge pixel modification process. In other implementations, a decoder receives metadata pertaining to edge pixel modification, which can be used to facilitate the decoding process.

In various implementations, supplementary data may be provided to a decoder within additional messages such as User Data Unregistered Supplementary Echo Intelligence (SEI) messages. Supplementary data may include metadata provided on a fragment or frame level. Supplementary data may include bitstream information indicating whether edge pixel modification has been performed, information identifying non-display pixels and/or display pixels, or other information to facilitate decoding by a decoder.

While the subject matter of this application has been particularly shown and described with reference to specific implementations thereof, it will be understood by those skilled in the art that changes in the form and details of the disclosed implementations may be made without departing from the spirit or scope of the invention. Examples of some of these implementations are illustrated in the accompanying drawings, and specific details are set forth in order to provide a thorough understanding thereof. It should be noted that implementations may be practiced without some or all of these specific details. In addition, well known features may not have been described in detail to promote clarity. Finally, although various advantages have been discussed herein with reference to various implementations, it will be understood that the scope of the invention should not be limited by reference to such advantages. Rather, the scope of the invention should be determined with reference to the appended claims. 

What is claimed is:
 1. A method, comprising: generating a two dimensional (2D) rectangular representation of virtual reality (VR) content by mapping VR content corresponding to a plurality of faces of a virtual three dimensional (3D) polygonal projection space to a 2D projection space, the VR content including one or more images corresponding to the plurality of faces of the virtual 3D polygonal projection space, the virtual 3D polygonal projection space corresponding to one of a hexahedron, a cube, an octahedron, a dodecahedron, or an icosahedron; identifying an edge within the 2D rectangular representation, the edge separating edge pixels of a first region within the 2D rectangular representation from edge pixels of a second region within the 2D rectangular representation, the edge pixels of the second region including at least a portion of display pixels of the second region and being immediately adjacent to the edge pixels of the first region, the edge pixels of the first region including at least a portion of non-display pixels of the first region, the display pixels containing image content of the VR content and the non-display pixels not containing image content of the VR content, the second region corresponding to one of the faces of the virtual 3D polygonal projection space, each of the display pixels and non-display pixels being represented by a corresponding set of pixel values including an intensity value; identifying at least a portion of the second region, the portion of the second region including at least one of: at least a portion of the edge pixels of the second region or a set of display pixels of the second region that are in close proximity to the edge; determining the intensity value for each of the display pixels of the portion of the second region within the 2D rectangular representation; for each of the non-display pixels of the first region within the 2D rectangular representation, determining a corresponding replacement intensity value based, at least in part, on the intensity value of at least one of the display pixels of the portion of the second region, the non-display pixels of the first region including the edge pixels of the first region; modifying the intensity value for each of the non-display pixels of the first region within the 2D rectangular representation to include the corresponding replacement intensity value such that modified non-display pixels are generated; and after modifying the intensity value for each of the non-display pixels of the first region within the 2D rectangular representation, encoding a plurality of pixels including the display pixels and the modified non-display pixels.
 2. The method as recited in claim 1, wherein the replacement intensity value for each of the non-display pixels mirrors, along at least one of a horizontal or vertical axis, the intensity value of a corresponding display pixel of a block of the second region.
 3. The method as recited in claim 1, wherein obtaining a replacement intensity value comprises: determining an average intensity value for the display pixels of the portion of the second region.
 4. The method as recited in claim 1, wherein the portion of the second region comprises a block of pixels defined by an encoder.
 5. The method as recited in claim 1, wherein the encoding is performed according to a variable block size such that the number of non-display pixels that are encoded in blocks that each contains at least a portion of the display pixels is minimized.
 6. A computer program product, comprising one or more non-transitory computer readable media having computer program instructions stored therein, the computer program instructions being configured such that, when executed by one or more processors, the computer program instructions cause the one or more processors to: obtain a two dimensional (2D) representation of virtual reality (VR) content corresponding to a plurality of faces of a virtual three dimensional (3D) projection space, the VR content including one or more images corresponding to the plurality of faces of the virtual 3D projection space; identify an edge within the 2D representation, the edge separating edge pixels of a first region within the 2D representation from edge pixels of a second region within the 2D representation, the edge pixels of the second region including at least a portion of display pixels of the second region and being immediately adjacent to the edge pixels of the first region, the edge pixels of the first region including at least a portion of non-display pixels of the first region, the second region corresponding to one of the faces of the virtual 3D projection space, the display pixels containing image content of the VR content and the non-display pixels not containing image content of the VR content, each of the display pixels and non-display pixels having an associated pixel value; identify at least a portion of the second region, the portion of the second region including at least one of: at least a portion of the edge pixels of the second region or a set of display pixels of the second region that are in close proximity to the edge; determine the pixel value for each of the display pixels of the portion of the second region; for each of the non-display pixels of the first region, determine a corresponding replacement pixel value based, at least in part, on the pixel value of at least one of the display pixels of the portion of the second region, the non-display pixels of the first region including the edge pixels of the first region; modify the pixel value of each of the non-display pixels of the first region to include the corresponding replacement pixel value such that modified non-display pixels are generated; and after modifying the pixel value for each of the non-display pixels of the first region, encode a plurality of pixels including the display pixels and the modified non-display pixels.
 7. The computer program product as recited in claim 6, wherein the pixel value comprises an intensity value.
 8. The computer program product as recited in claim 6, wherein the replacement pixel value for each of the non-display pixels mirrors, along at least one of a horizontal or vertical axis, the pixel value of a corresponding display pixel of a block of the second region.
 9. The computer program product as recited in claim 6, wherein obtaining a replacement pixel value comprises: determining an average pixel value for the display pixels of the portion of the second region.
 10. The computer program product as recited in claim 6, wherein the portion of the second region comprises a block of pixels defined by an encoder.
 11. The computer program product as recited in claim 6, wherein the computer program instructions are further configured to cause the one or more processors to: encode the plurality of pixels according to a variable block size such that the number of non-display pixels that are encoded in blocks that each contains at least a portion of the display pixels is minimized.
 12. The computer program product as recited in claim 6, wherein the computer program instructions are further configured to cause the one or more processors to: after modifying the pixel value for each of the non-display pixels of the first region, instruct an encoder to encode the plurality of pixels including the display pixels and the modified non-display pixels according to a specified block size.
 13. The computer program product as recited in claim 6, wherein the 3D projection space comprises a polygonal projection space, and wherein the polygonal projection space corresponds to one of a hexahedron, a cube, an octahedron, a dodecahedron, or an icosahedron.
 14. A system, comprising: an encoder configured to encode video frames according to a particular encoding standard; and one or more processors and memory configured to: obtain a two dimensional (2D) representation of virtual reality (VR) content corresponding to a plurality of faces of a virtual three dimensional (3D) projection space, the VR content including one or more images corresponding to the plurality of faces of the virtual 3D projection space; identify an edge within the 2D representation, the edge separating edge pixels of a first region within the 2D representation from edge pixels of a second region within the 2D representation, the second region corresponding to one of the faces of the virtual 3D projection space, the edge pixels of the second region including at least a portion of display pixels of the second region and being immediately adjacent to the edge pixels of the first region, the edge pixels of the first region including at least a portion of non-display pixels of the first region, the display pixels containing image content of the VR content and the non-display pixels not containing image content of the VR content, each of the display pixels and non-display pixels having an associated pixel value; identify at least a portion of the second region, the portion of the second region including at least one of: at least a portion of the edge pixels of the second region or a set of display pixels of the second region that are in close proximity to the edge; determine the pixel value for each of the display pixels of the portion of the second region; for each of the non-display pixels of the first region, determine a corresponding replacement pixel value based, at least in part, on the pixel value of at least one of the display pixels of the portion of the second region, the non-display pixels of the first region including the edge pixels of the first region; modify the pixel value of each of the non-display pixels of the first region to include the corresponding replacement pixel value such that modified non-display pixels are generated; and after modifying the pixel value for each of the non-display pixels of the first region, encode, by the encoder, a plurality of pixels including the display pixels and the modified non-display pixels.
 15. The system as recited in claim 14, wherein the pixel value comprises an intensity value.
 16. The system as recited in claim 14, wherein the replacement pixel value for each of the non-display pixels mirrors, along at least one of a horizontal or vertical axis, the pixel value of a corresponding display pixel of a block of the second region.
 17. The system as recited in claim 14, the processors and memory being further configured to: obtain the replacement pixel value by determining an average pixel value for the display pixels of the portion of the second region.
 18. The system as recited in claim 14, wherein the portion of the second region comprises a block of pixels defined by the encoder.
 19. The system as recited in claim 14, the processors and memory being further configured to: encode the plurality of pixels including the display pixels and the modified non-display pixels according to a variable block size such that the number of non-display pixels that are encoded in blocks that each contains at least a portion of the display pixels is minimized.
 20. The system as recited in claim 14, wherein the 3D projection space comprises a polygonal projection space, and wherein the polygonal projection space corresponds to one of a hexahedron, a cube, an octahedron, a dodecahedron, or an icosahedron.
 21. The system as recited in claim 14, the processors and memory being further configured to: provide metadata to the encoder, the metadata indicating at least one of: regions within the 2D representation containing display pixels, regions within the 2D representation containing non-display pixels, or regions within the 2D representation containing modified pixels.
 22. The system as recited in claim 14, the processors and memory being further configured to: after modifying the pixel value for each of the non-display pixels of the first region, instruct the encoder to encode the plurality of pixels.
 23. The system as recited in claim 14, the edge being diagonal.
 24. The method as recited in claim 1, wherein modifying the intensity value for each of the non-display pixels of the first region within the 2D rectangular representation comprises: modifying the intensity value for each of the edge pixels of the first region to include the corresponding replacement intensity value. 